I did my first ever oil change last night and it all went well. I also changed the oil filter, remembering advice written on here to carefully check how it fits together as I took it apart, so that I could reassemble it properly. The oil was changed, I took the car for a short (5 mile) run and checked for leaks and it all looks good with no sign of escaping oil.
However, once home I did a bit of digging online and found this diagram from Moss:

I note that my filter housing did not contain the washer / seal / clip numbered 126, 127 and 128 on the diagram. All other components were there and reassembled correctly. Will I have problems with these parts being missing? If so, do I need to buy them and fit them ASAP - which would mean changing the oil again?
Thanks in advance
James